1. Field of the Invention
This invention relates generally to permanent gray-scale reproductions and more particularly relates to permanent reproductions of half-tone monochrome images.
2. Description of the Prior Art
Reproductions such as photographic prints and ink-based prints degrade significantly upon exposure to light, extremes of temperature, chemical corrosion, and active biological agents. Significant quality degradation may occur in days to decades depending on the nature of the ambient. When such reproductions are used outdoors, they must either be renewed periodically or suitably sealed. Sealing in general deteriorates image quality as the integrity of the seal increases, and does not preclude photochemical and thermal degradation.
The best-known alternative reproduction technique for enhanced lifetime is metal-based intaglio. By stamping or chemical-etching a metallic background material, images of limited quality may be reproduced. Only etching is practical for fine detail. Neither stamping nor etching is compatible with refractory background materials, so there is a fundamental tradeoff between image quality (e.g. resolution) and permanence in this technology. In addition, the image is reproduced by textural variations and thus does not have a true gray-scale.